1. Field of the Invention
The present invention relates to refrigeration and heat pump systems and more particularly to an absorption refrigeration cycle of the generator-absorber heat exchange ("GAX") type. The invention is especially adapted for use in a gas-fired, air-to-air, absorption heat pump.
2. Description of Related Art
Absorption refrigeration cycles were developed in the mid 1800's and were used primarily in refrigeration systems. Such cycles operated by using a refrigerant/absorbent mixture, the refrigerant vapor being absorbed in an absorber into a liquid absorbent, thus producing heat, followed by heating the refrigerant/absorbent mixture in a generator to drive off the refrigerant vapor. A condenser, which also produced heat, and an evaporator, which extracted heat, completed the cycle. The heat produced by absorption in the absorber was discarded, along with that from the condenser, to a coolant, generally cooling water.
These early "single stage" absorption cycle systems were energy inefficient but were often preferred to compression systems, before the advent of electric motors, because the cost of heat energy to operate them was low and they required much less mechanical energy than compression systems. For most applications, the use of these single stage absorption systems declined with changes in the relative cost of gas and electric energy and improvements in electrically operated compression systems. However, even today, these relatively inefficient single stage systems are still in use in low pressure lithium bromide commercial air conditioning systems and in refrigeration systems for recreational vehicles and hotel rooms.
In 1913, an improved absorption cycle was devised by Altenkirch. This cycle was made more efficient than the early single stage cycles by transferring a portion of the heat produced in the absorber to the refrigerant/absorbent fluid circulated to the generator, and transferring to the generator a portion of the heat in the absorbent flowing from the generator to the absorber. This transfer of heat reduced the heat input required to the generator to evaporate the refrigerant from the refrigerant/absorbent mixture. This system has been called the absorber heat exchange (AHE) system.
The AHE cycle was used in the early 1960's to produce absorption systems that were efficient enough to be cost effective air conditioners at that time. The AHE cycle has been used in residential, air cooled air conditioners, starting in 1965. However, even in these AHE systems, a large portion of the heat generated by the absorption process in the absorber was lost. The AHE cycle was also used experimentally in air-to-air gas heat pumps, which were also advantageous in heating, but were never commercially produced. As energy costs have increased, the AHE air conditioners have lost much of their operating cost advantages and today, have only a limited market.
Also in 1913, Altenkirch devised another absorption cycle that recovered more of the heat of absorption from the absorber. This cycle, which has come to be known as the generator-absorber heat exchange (GAX) cycle, utilized an additional heat exchange system, whereby high temperature heat produced by the absorption process in the absorber was transferred via a heat exchange fluid to the generator. This GAX cycle concept is capable of recovering an additional large amount of heat from the absorber and capable of utilizing higher generator temperatures than the AHE system and thus is capable of achieving much higher energy efficiencies. The heating efficiency of such GAX systems, relative to the particular fuel used, can be much higher than that of furnaces, boilers, etc.
However, prior art GAX cycle systems suffered from the disadvantage that a separate heat transfer circuit using a separate heat transfer fluid was required. This heat transfer circuit had to be hermetic, required an expansion chamber, required a hermetic pump capable of variable flow, and required a system to control the amount of flow of the heat transfer fluid to match the GAX heat to be transferred in either the cooling or heating cycle at the particular outdoor temperature. Also, using a fluid in the heat transfer circuit different from the working fluid created the danger of cross-contamination between the heat transfer circuit and the absorber or generator. These prior art GAX systems typically used a heat transfer fluid that remained in the liquid phase and thus could only use the sensible heat of the heat transfer liquid.
Electric heat pumps, which operate with a standard condenser-evaporator cycle, have heretofore been utilized for residential and small commercial heating and cooling applications. However, while electric heat pumps can effectively satisfy the heating and cooling requirements of residential and small commercial buildings in areas having relatively warm climates, such as the southern states of the United States, these electric heat pumps are not capable of providing, without auxiliary heating equipment, the necessary heating in climates where the temperatures drop below about 30.degree. F. In addition, these electric heat pump systems typically use refrigerants that may be hydrochlorofluorocarbons (HCFC's) or chlorofluorocarbons (CFC's), which are environmentally hazardous.
Thus, the need exists for a generator-absorber heat exchange apparatus and method suitable for use in a residential or small commercial heat pump that efficiently transfers a large portion of the heat produced by the absorption process in the absorber to the generator without the use of a costly, possibly failure prone, independent heat transfer circuit.
The instant invention satisfies that need by providing a generator-absorber heat exchange apparatus and method that can use an environmentally safe fluid as both the working fluid and the heat exchange fluid, that efficiently recovers a large proportion of the heat generated by the absorption process in the absorber, that does not require an elaborate system of controls, that advantageously may use either or both the latent heat and the sensible heat of the working fluid to transfer heat from the absorber to the generator by operating between its vapor and liquid phases, and that, because of size, cost and efficiency, can be used to satisfy residential and commercial heating and cooling requirements over a wide range of climates, including sufficient heating at temperatures below 0.degree. F.
Additional features and advantages of the invention will be set forth in the drawings and written description which follow, and in part will be apparent from the drawings and written description or may be learned from the practice of the invention. The advantages of the invention will be realized and attained by the generator-absorber heat exchange apparatus, the heat pump incorporating the generator-absorber heat exchange apparatus and the method for transferring heat between an absorber and generator in a generator-absorber heat exchange apparatus, particularly pointed out in the drawings, written description and claims hereof.